Polyester composition and film made therefrom

ABSTRACT

The invention is a polyester composition containing crosslinked polymer particles with ester bonds at the main chain. The particles are excellent in affinity to polyesters, and so the films formed from the polyester compositions do not have the particles falling off during high speed running, and do not have flaws in the film surfaces. The invention can prevent the generation of white powder and the flaws of magnetic faces caused by falling-off particles, and prevent the contamination in the production of films, even though these are problems caused when various conventional particles are added, and is especially suitable for use as products such as magnetic films.

TECHNICAL FIELD

The present invention relates to polyester compositions and films madetherefrom excellent in abrasion resistance and magnetic surface flawpreventability when the films run at high speeds.

BACKGROUND ART

In general, polyesters such as polyethylene terephthalate are excellentin mechanical properties and chemical properties, and are widely used asformed products such as films and fibers. When the polyesters areprocessed and used as formed products, their slipping property andabrasion resistance greatly affect the workability in their productionand various applications. For example, if a polyester tape insufficientin such properties is used as a base film for producing a magnetic tape,the friction between the coating roll and the film during magnetic tapeproduction becomes large, thereby wrinkling or scratching the film.Moreover, the film is liable to be abraded to generate powder, and whenthe film is coated with a magnetic layer, it may have portions devoid ofthe magnetic layer, and as a result, missing of magnetic recording(drop-out) is likely to occur. Furthermore, as a recently identifieddisadvantage, when the film is wound after completion of calendering inthe step of magnetic layer coating, the magnetic face is rubbed by thenon-magnetic face, to be flawed, thereby causing quality deteriorationsuch as drop-out in use as a product.

For improving the slipping property of a film, many proposals have beenmade for letting polyesters contain inorganic particles such as titaniumdioxide, calcium carbonate and silicon dioxide. However, theseinorganics particles which are low in affinity to polyesters easily falloff, producing scrapings, degrading in slipperiness or suffering fromflaws on the surface, when an external force acts during use, forexample, as a film, due to contact with rolls during calendering in thestep of magnetic layer coating or during film running or due tointer-layer contact of the film during winding. If such scrapings areproduced in large amounts or the surface is flawed, it would lead toimperfect formation of the magnetic layer during the coating process andthe film may suffer from drop-outs during use. Furthermore, if thecalender roll used in the step of magnetic layer coating is soiled, theworkability in the production of magnetic recording film is remarkablylowered. Thus it has been hoped that the properties of these magneticlayers may be improved so that they do not suffer from flaws andabrasion due to low affinity to polyesters.

Methods proposed for improving the affinity between the particles andpolyesters include the surface treatment of inorganic particles, the useof organic particles, etc. Conventional methods regarding surfacetreatment of inorganic particles include the surface treatment bypolyacrylic-acid-based polymers proposed in Japanese Patent Laid-Open(Kokai) No. 63-128031, the surface treatment by phosphorus-containingcompounds proposed in Japanese Patent Laid-Open (Kokai) Nos. 62-235353and 63-234039, the surface treatment by coupling agents proposed inJapanese Patent Laid-Open (Kokai) Nos. 62-223239 and 63-312345, thesurface treatment by silane compounds proposed in Japanese PatentLaid-Open (Kokai) No. 63-304038 and the surface treatment by graftingusing a glycol proposed in Japanese Patent Laid-Open (Kokai) No.88-280763. However, even these methods cannot achieve sufficientabrasion resistance since it is difficult to obtain satisfactoryaffinity because the particles used are inorganic.

For organic particles, various kinds are proposed, for example, inJapanese Patent Laid-Open (Kokai) No. 49-117550 (polyethyleneterephthalate particles and poly-1,4-bis(hydroxymethyl)-cyclohexaneterephthalate particles), Japanese Patent Laid-Open (Kokai) No. 50-14748(polyethylene naphthalate resin), Japanese Patent Laid-Open (Kokai) No.54-132652 (polyphenyl ester resin), etc. However, since these particlesare of linear polymers without crosslinking structure, they areinsufficient in heat resistance, and the thermal history of hightemperatures inflicted during the production of polyesters and filmsmakes the particles poorly stable, thereby disadvantageously notallowing the films to be sufficiently resistant against abrasion.Furthermore, organic particles with crosslinked structure are proposed,for example, in Japanese Patent Laid-Open (Kokai) No. 59-217755(crosslinked polymer particles sharp in grain size distribution),Japanese Patent Laid-Open (Kokai) No. 61-174254 (crosslinked polymerparticles capable of reacting with polyesters) and Japanese PatentLaid-Open (Kokai) No. 2-189359 (vinyl compound/divinylbenzene copolymerparticles, dicarboxylic acid/acrylate copolymer particles, etc.), etc.However, a problem of these particles is that they are not ofpolyesters, even though they are relatively high in heat resistance.Since ester bonds do not exist at the main chain of the polymer formingthe particles, the polymer cannot exhibit its affinity with thepolyester used as the matrix, and the film containing them cannot havehigh abrasion resistance when it runs at a high speed.

The inventors studied intensively, and as a result, found that particlesmade of a crosslinked polymer with ester bond at its main chain are veryhigh in affinity with polyesters, and that films containing them areremarkably higher in abrasion resistance and magnetic face flawpreventability when they are run at high speeds. The object of thepresent invention is to overcome the above mentioned disadvantages ofthe prior art, and to present polyester composition excellent inabrasion resistance and magnetic face flaw preventability when the filmsformed from them are run at high speeds.

DISCLOSURE OF THE INVENTION

The present invention is a polyester composition comprising particlesmade of crosslinked polymer with ester bond at its main chain, and alsoa film made of the polyester composition.

BEST MODE FOR CARRYING OUT THE INVENTION

The crosslinked polymer used for forming the particles of the presentinvention is not especially limited as far as it has ester bond at itsmain chain and a crosslinked structure. The polymers with ester bond atthe main chain used for forming the particles include, for example,polyesters composed of a polybasic acid and a polyhydric alcohol andpolyphenyl esters composed of a phenyl ester and a polyhydric alcohol.Especially a polyester composed of a polybasic acid and a polyhydricalcohol is preferable.

The particles made of a crosslinked polymer with such a main chain canbe, as one type, particles made of an unsaturated polyester resincrosslinked by a compound with an aliphatic unsaturated bond. Anunsaturated polyester can be prepared from a dicarboxylic acid or any ofits ester formable derivatives (A), a glycol (B) and a compound with analiphatic unsaturated bond capable of crosslinking the unsaturatedpolyester (C). In this case, it is necessary that at least eithermonomer of the dicarboxylic acid or any of its ester formablederivatives (A) or the glycol (B) has an aliphatic unsaturated bond.

The dicarboxylic acid (A) as a compound with an aliphatic unsaturatedbond may be such as substance as maleic acid or its anhydride,methylmaleic acid, fumaric acid, methylfumaric acid, glutaconic acid,acetylenedicarboxylic acid, 2-butyne-1,4-dicarboxylic acid, and theirester formable derivatives. Among them, maleic acid or its anhydride andfumaric acid are preferable. On the other hand, the glycol (B) may besuch a substance as propenediol, butenediol, hexenediol,dimethylhexenediol, hexadienediol, hexadiynediol, octadiynediol,acetylenediol, etc., and their ester formable derivatives. Among them,propenediol, butenediol and hexenediol are preferable.

The compound (C) with an aliphatic unsaturated bond capable ofcrosslinking the unsaturated polyester may be, for example, an aromaticmonovinyl compound such as styrene, α-methylstyrene, chlorostyrene,fluorostyrene, ethylvinylbenzene, vinyltoluene and vinylpyridine etc.,divinyl compounds such as divinylbenzene, diallylphthalate and divinylether etc., vinyl cyanide compounds such as acrylonitrile andmethacrylonitrile etc., acrylates or acrylic esters such as methylacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hydroxyethylacrylate, glycidyl acrylate and vinylacetate methyl acrylate,methacrylates or methacrylic esters such as methyl methacrylate, ethylmethacrylate, propyl methacrylate, butyl methacrylate,allylmethacrylate, phenylmethacrylate, hydroxyethyl methacrylate,glycidyl methacrylate and vinylacetate methyl methacrylate, polyvalentacrylates such as ethylene glycol diacrylate, butylene glycoldiacrylate, polyethylene glycol diacrylate, diglycidyl ether diacrylateand trimethylolpropane triacrylate, polyvalent methacrylates such asethylene glycol dimethacrylate, butylene glycol dimethacrylate,polyethylene glycol dimethacrylate, diglycidyl ether dimethacrylate andtrimethylolpropane trimethacrylate, amide monomers such as acrylamideand methacrylamide, and acetylene compounds such as methylacetylene,ethylacetylene, dimethylacetylene and diethylacetylene. Among them,aromatic monovinyl compounds, divinyl compounds, acrylates,methacrylates, acrylic esters, methacrylic esters, polyvalent acrylatesand polyvalent methacrylates are preferable.

The unsaturated polyester resin of the present invention can also beformed by respectively plural compounds of (A), (B) and (C).Furthermore, the compound (A) may partially include a saturateddicarboxylic acid or the compound (B) may partially include a saturatedglycol. The saturated dicarboxylic acid may be such a substance asterephthalic acid, 2,6-naphthalenedicarboxylic acid,diphenyldicarboxylic acid, isophthalic acid, phthalic acid, succinicacid, adipic acid, sebacic acid or their ester formable derivatives etc.Among these saturated dicarboxylic acids, terephthalic acid,2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, isophthalicacid and their ester formable derivatives are preferable. Furthermore,the saturated glycol may be such a substance as ethylene glycol,diethylene glycol, butylene glycol, propylene glycol, dipropyleneglycol, trimethylene glycol, tetramethylene glycol, pentyl glycol,neopentyl glycol, hexamethylene glycol, polyethylene glycol,cyclohexanedimethanol, bisphenol A, bisphenol S or their hydrognatedcompounds etc. Among these saturated glycols, ethylene glycol,cyclohexanedimethanol, bisphenol A and bisphenol S are preferable. Theamount of the saturated dicarboxylic acid or saturated glycol should bepreferably 80 mol % or less, more preferably 70 mol % or less againstall the carboxylic acid components or all the glycol components in viewof the heat resistance of the particles.

The above mentioned unsaturated polyester resin in the present inventioncan be prepared by any conventional process. For example, after a linearpolyester with aliphatic unsaturated bonds is prepared from the compound(A) and the compound (B), the compound (C) is caused to react forcrosslinking it by suspension polymerization. In this case, the esterinterchange or esterification between the compounds (A) and (B) isfollowed by condensation polymerization, to prepare the intendedpolyester with aliphatic unsaturated bonds. Then, the polyester and thecompound (C) are suspended and dispersed into a solvent such as waterwhich does not dissolve them at all or little dissolves them, andfurthermore any known catalyst, for example, an organic peroxide such asbenzoyl peroxide, ethyl methyl ketone peroxide or lauroyl peroxide isadded for polymerization, to obtain a crosslinked polymer resin. Thepreparation of the unsaturated polyester resin by suspensionpolymerization as described above is preferable because of suchadvantages that the affinity with polyesters can be specificallyenhanced, that the particles contain less impurities such as emulsifyingagent and that the particle size can be easily controlled.

The crosslinked polymer particles of the present invention can also beprepared by the following emulsion polymerization methods, instead ofthe above described suspension polymerization method.

(a) Soap-free polymerization method, in which no emulsifying agent or avery small amount of an emulsifier is used for polymerization.

(b) Seed polymerization method, in which polymer particles are addedinto the polymerization system prior to emulsion polymerization.

(c) Core-shell polymerization method, in which a part of monomercomponents are emulsion-polymerized and the remaining monomer componentsare polymerized in the same polymerization system.

(d) Polymerization methods employing the Ugelstad, etc. disclosed inJapanese Patent Laid-Open (Kokai) Nos. 54-97582 and 54-126288.

(e) Polymerization methods without using any swelling assistant in themethods of (d).

The particles made of a crosslinked polymer with ester bonds at its mainchain in the present invention can also be, as another preferable type,the particles of a polyester resin with a polyhydric alcohol (D) and apolybasic acid (E) as main components, at least either of the componentsbeing tri- or higher-valent.

The polyhydric alcohol (D) refers to a compound with at least two ormore hydroxyl groups in one molecule, and may be such a substance asethylene glycol, diethylene glycol, butylene glycol, propylene glycol,dipropylene glycol, trimethylene glycol, tetramethylene glycol,hexamethylene glycol, pentyl glycol, neopentyl glycol, polyethyleneglycol, cyclohexanedimethanol, bisphenol A, bisphenol S or theirhydrogenated compounds, and furthermore the tri- or higher-hydricalcohol may be such a substance as glycerol, trimethylolethane,trimethylolpropane, trimethylolbutane, trimethylolbenzene, hexanetriol,pentaerythritol, sorbitol, tetramethylolcyclohexanol, etc. Among them,especially, ethylene glycol, butylene glycol, hexamethylene glycol,polyethylene glycol, cyclohexanedimethanol, bisphenol A, bisphenol S,glycerol, trimethylolpropane and pentaerythritol are preferable.

The polybasic acid (E) refers to a compound with at least two or morecarboxyl groups in one molecule, and may be, for example, an aromaticdicarboxylic acid such as terephthalic acid, isophthalic acid,napthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid,diphenyldicarboxylic acid and phthalic acid, aliphatic dicarboxylicacids such as adipic acid, sebacic acid, dimeric acid, maleic acid,maleic anhydride, fumaric acid, oxalic acid and succinic acid, alicyclicdicarboxylic acids such as cyclohexanedicarboxylic acid, or their esterformable derivatives etc. Furthermore, the tri- or higher-carboxylicacid may be such a substance as hemimellitic acid, trimesic acid,trimellitic acid, prehnitric acid, pyromellitic acid, mellophanic acid,or their ester formable derivatives, etc. Among the polybasic acids (E)enumerated above, terephthalic acid, isophthalic acid,naphthalenedicarboxylic acid, diphenyldicarboxylic acid, adipic acid,sebacic acid, maleic acid, maleic anhydride, fumaric acid, succinicacid, trimesic acid, trimellitic acid, pyromellitic acid or their esterformable derivatives are preferable.

Furthermore, the crosslinked polymer can also be formed by using pluralcompounds of polyhydric alcohol (D) or polybasic acid (E).

The crosslinked polymer particles composed of the polyhydric alcohol (D)and the polybasic acid (E) in the present invention can be prepared byany conventional method for preparing polyester resins. That is, theparticles can be prepared by transesterification or esterification ofthe polyhydric alcohol (D) and the polybasic acid (E), and subsequentcondensation polymerization.

In the crosslinked polymer particles of the present invention, thecrosslinking degree defined by the following formula (1) for all theorganic components forming the particles should be preferably 1 wt % ormore.

    Crosslinking degree=(Weight of crosslinked component in raw monomers)/(Total weight of raw monomers)×100(%)     (1)

A preferable degree is 5 wt % or more, and a more preferable degree is10 wt % or more. When the crosslinking degree is kept in this range, theparticles can be elastic, to stabilize the protrusion forms in the film,for improving the slipperiness and abrasion resistance in the high speedrunning of the film. Moreover, as described later, the thermaldecomposition temperature of the particles can be raised, and in thiscase, preferably it cannot happen that the particles are agglomerated toimpair the film surface uniformness, abrasion resistance, etc. duringthe production of the polyester composition, during its melt molding orin the recycled re-utilization of formed products.

The crosslinked polymer particles of the present invention can bestructurally uniform or non-uniform or even hollow. In the case ofnon-uniform structure, for example, two or more structural patterns maybe mixed. For example, the core of each particle and the external layeraround it may be different in the kind and quantity of thenon-crosslinked component and in the kind and quantity of thecrosslinked component. Moreover, each particle may have portionsdifferent in composition from the particle itself dispersed.

The crosslinked polymer particles in the present invention should bepreferably 0.01 to 5 μm, more preferably 0.03 to 1 μm in averagediameter, and should be contained in the polyester composition bypreferably 0.005 to 10 wt %, more preferably 0.01 to 5 wt % based on theweight of the polyester composition. When the average diameter of theparticles and the content in the polyester composition are kept in theabove respective ranges, the film made of it can exhibit slipperinessand abrasion resistance. The average diameter in this case refers to anumber average diameter obtained by photographing the particles in apolymer or film by an electron microscope at a magnification of about20,000 to 50,000 times (30 photos of 8 cm×10 cm in size), and measuringand calculating the equivalent sphere diameters of the particles. Theequivalent sphere diameter refers to a diameter of a sphere with avolume equal to that of a particle.

To prepare such fine crosslinked polymer particles, in the case ofparticles made of an unsaturated polyester resin, for example, thedispersion medium of the monomers can be stirred at a high speed forsuspension polymerization. On the other hand, in the case of particlescomposed of a polyhydric alcohol and a polybasic acid, the crosslinkedpolymer resin can be ground by a medium type mill such as roll mill,sand mill or ball mill, or furthermore classified using a decanter, etc.

If the crosslinked polymer particles of the present invention are morethan 1.1 to less than 5.0 in ratio Dw/Dn, where Dw is the weight averagediameter and Dn is the number average diameter, the film obtained ispreferably good in slipperiness and abrasion resistance. The weightaverage diameter and the number average diameter in this case areobtained by photographing the particles in a polymer or film by anelectron microscope at a magnification of about 20,000 to 50,000 times(30 photos of 8 cm×10 cm in size), and measuring and calculating theequivalent sphere diameters of the particles. The equivalent spherediameter refers to a diameter of a sphere with a volume equal to that ofa particle.

As for the heat resistance of the crosslinked polymer particles, thethermal decomposition temperature (10% weight loss temperature) of theparticles measured by a thermobalance should be preferably 350° C. orhigher, more preferably 360° C. or higher, further more preferably 380°C. or higher. In this case, preferably it cannot happen that theparticles are agglomerated to impair the film surface uniformness,abrasion resistance, etc. during the production of the polyestercomposition, during its melt molding or in the recycled re-utilizationof formed products.

In the present invention, to obtain films good in transparency andabrasion resistance, the crosslinked polymer particles should bepreferably 20 to 95% in the porosity obtained from the following formula(2) in reference to the pore volume of each particle measured by amercury porosimeter and to the specific gravity of the particle.

    Porosity(%)=Pore volume/{(1/Specific gravity)+Pore volume}×100 (2)

A more preferably porosity is 30 to 80%, and a further more preferablyporosity is 40 to 70%. If the porosity is less than 20%, the film formedhas voids to impair transparency, slipperiness and abrasion resistance,and if more than 95%, the particles are poor in form stability.

It is preferable that the crosslinked polymer particles of the presentinvention are treated on the surfaces by a compound with an alkali metalsalt of a functional groups such as carboxyl group, to ensure both goodaffinity with polyesters and good dispersion property. The alkali metalsalt of carboxyl group can be selected from sodium salt, potassium salt,lithium salt, etc., and among them, sodium salt of carboxyl group ispreferable in view of higher affinity. The chemical species with afunctional group for introducing the alkali metal salt of carboxyl groupcan be either a monomer or a polymer, and is not especially limited.Above all, methacrylic acid, acrylic acid and their polymers arepreferable. Moreover, the chemical species with a carboxyl group mayalso be copolymerized with a chemical species without any functionalgroup or a chemical species with any other functional group thancarboxyl group. In this case, in view of heat resistance, a styrenecompound is preferable. The method for introducing the alkali metal saltof carboxyl group is not especially limited, but in view of heatresistance of the particles, it is preferable to one produce thecrosslinked polymer particles and then to add a surface treating agent,for adsorption or reaction on the surfaces. For example, to introduce Namethacrylate, at first the crosslinked polymer particles are producedand subsequently styrene or methacrylic acid is added for partialpolymerization, to keep the system on the alkali side, so that --COONagroup by Na methacrylate may be introduced into the surfaces of theparticles. The amount of the surface treating agent should be preferably0.01 to 20 wt %, more preferably 0.1 to 10 wt % based on the weight ofthe particles.

In the present invention if at least one ore more kinds of conventionalinorganic particles and organic particles are contained in addition tothe crosslinked polymer particles, the film running ability and abrasionresistance can be improved preferably. The compound of the inorganicparticles can be selected, for example, from inorganic oxides such asaluminum oxide, zirconium oxide and silicon oxide, inorganic carbonatessuch as calcium carbonate and barium carbonate, inorganic phosphatessuch as calcium phosphate and sodium phosphate, inorganic sulfates suchas barium sulfate and calcium sulfate, inorganic mixed oxides such askaolin and talc, fluorides such as fluorite, and also potassiumtitanate, aluminum hydroxide, etc. The organic particles can be selectedfrom silicone particles, teflon particles, polyimide particles, etc.Among them, titanium oxide, silicon oxide, calcium carbonate, zirconiumoxide, aluminum oxide and silicone particles are preferable. The averagediameter of these inorganic particles and organic particles should bepreferably 0.001 to 3 μm, more preferably 0.002 to 2 μm. Their contentshould be preferably 0.001 to 20 wt %, more preferably 0.002 to 15 wt %based on the weight of the polyester composition. Furthermore, inaddition to the above inorganic and organic particles, it is alsopossible to additionally use non-incorporated particles composed of atleast one of aromatic carboxylates, alkali metals and alkaline earthmetals, and a phosphorus compound, which are precipitated in thereaction system in the production of the polyester.

In the present invention, the crosslinked polymer particles andinorganic particles can be added to be contained in the polyester, byany conventional method, for example, by adding as a powder or glycolslurry into the reaction system of the polyester, or kneading as apowder or a slurry using a low boiling-point solvent into the polyester.Especially the crosslinked polymer particles of the present inventionshould be preferably kneaded as a slurry with the particles in waterand/or in an organic compound of 200° C. or lower in boiling point intothe polyester by a vent-type molding machine, in view of the uniformdispersion of the particles. In this case, carrying out melt kneadingafter removing the water and/or organic compound of 200° C. or lower inboiling point by heating under reduced pressure is preferable since thedispersiblity of the particles can be improved. The vent-type moldingmachine refers to a melt molding machine with at least one vent hole,and can be, for example, an extruder or injection molding machine. Atleast one of the vent holes for removing the water and/or organiccompound of 200° C. or lower in boiling point must be kept under reducedpressure. The vent hole should be preferably kept at a reduced pressureof 100 Torrs or less, more preferably at 50 Torrs or less, further morepreferably at 30 Torrs or less.

When the crosslinked polymer particles of the present invention areadded to the polyester as a slurry of water and/or an organic compoundof 200° C. or less in boiling point, the organic compound of 200° C. orlower in boiling point is not especially limited and can be selected,for example, from alcohols such as methanol, ethanol and ethyleneglycol, hydrocarbons such as benzene and toluene, and also esters,ketones, amines, etc. Among them, water is preferable in view ofhandling, removability, etc. Of course, the water and/or organiccompound of 200° C. or lower in boiling point can be a mixed solventconsisting of two or more solvents. In this case, a water-rich mixedsolvent is preferably.

The slurry of the crosslinked polymer particles can preferably containan anionic interfacial active agent such as sodium dodecylbenzenesulfonate or sodium lauryl sulfate, a nonionic interfacial active agentsuch as polyoxyethylene nonyl phenyl ether or polyethylene glycolmonostearate, a dispersing agent such as polyvinyl pyrrolidone,polyvinyl alcohol or carboxymethyl cellulose.

The concentration of the slurry with the crosslinked polymer particlesin water and/or organic compound of 200° C. or lower in boiling point isnot especially limited. However, it is preferable that the amount of thewater and/or organic compound of 200° C. or lower in boiling point addedis 2 to 30 wt %, more preferably 2 to 20 wt % based on the weight of thepolymer, and in this case, the dispersibility of the particles in thepolymer is good, and the intrinsic viscosity of the polymer is notlowered preferably.

The crosslinked polymer particles of the present invention can also bedispersed into the glycol component used as a raw material of thepolyester, to make a slurry, and adding the slurry at any optional stagebefore the completion of polyester production, instead of being kneadedinto the polyester as a slurry with the particles in water and/ororganic compound of 200° C. or lower in boiling point by a vent typemolding machine as described above.

The polyesters used in the present invention is produced from adicarboxylic acid with an aromatic dicarboxylic acid as the main acidcomponent or any of its ester formable derivatives and a glycol, andmainly include polyalkylene terephthalate, polyalkylene naphthalate,etc. Among these polyesters, polyethylene terephthalate andpolyethylene-2,6-napthalate are especially preferably.

The polyesters of the present invention can be either homopolyesters orcopolyesters. The comonomer for the copolyesters can be selected, forexample, from aromatic dicarboxylic acids such as terephthalic acid,isophthalic acid, naphthalenedicarboxylic acid, 5-sulfoisophthalic acid,diphenyldicarboxylic acid and phthalic acid, aliphatic dicarboxylicacids such as adipic acid, sebacic acid, dimeric acid, maleic acid,fumaric acid, oxalic acid and succinic acid, alicyclic dicarboxylicacids such as cyclohexanedicarboxylic acid, aliphatic glycols such asethylene glycol, propanediol, butanediol, pentanediol, hexanediol,neopentyl glycol, diethylene glycol and polyethylene glycol, aromaticglycols such as bisphenol A and bisphenol S, alicyclic glycols such ascyclohexanedimethanol, polyfunctional compounds such as trimelliticacid, trimesic acid and trimethylolpropane and oxycarboxylic acids suchas p-hydroxybenzoic acid. One or more in combination of these comonomerscan be used.

The polyesters of the present invention can be produced by an optionalconventional method. In the case of producing polyethyleneterephthalate, for example, dimethyl terephthalate and ethylene glycolmay be transesterified in the presence of a catalyst, followed bycondensation polymerization at a high temperature under reduced pressurein the presence of a polymerization catalyst. As another method,esterification of terephthalic acid and ethylene glycol can be followedby condensation polymerization. In this case, it is preferable to add acoloring preventive agent such as a phosphorus compound at any optionalstage before completion of condensation polymerization and preferablyafter completion of ester interchange or esterification. As a furtherother method, solid state polymerization can be used, in which aftercompletion of ester interchange or esterification, condensationpolymerization is effected up to a certain degree of polymerization,being followed by further condensation polymerization with the obtainedpolymer kept at a temperature lower than its melting point under reducedpressure or in inactive gas current.

The production of the polyesters of the present invention allows the useof conventional ester interchange catalysts, condensation polymerizationcatalysts and coloring preventive agents. The ester interchangecatalysts include, for example, aliphatic carboxylates of alkaline earthmetals, zinc, maganese and alkali metal compound, halogenide and metalglycolates, etc., concretely, manganese acetate, magnesium acetate,calcium acetate, zinc acetate, lithium acetate, potassium acetate,sodium acetate, magnesium propionate, manganese propionate, potassiumpropionate, calcium propionate, zinc propionate, magnesium chloride,lithium chloride, manganese bromide, magnesium hydroxide, manganesehydroxide, calcium hydroxide, zinc hydroxide, lithium hydroxide,magnesium glycolate, calcium glycolate, lithium methylate, butylpotassium, etc. The condensation polymerization catalysts include forexample, antimony compounds such as antimony trioxide, germaniumcompounds such as germanium dioxide, and titanium compounds such astetrabutyl titanate. The coloring preventive agents include phosphoruscompounds such as phosphates, monomethyl phosphate, dimethyl phosphate,trimethyl phosphate, tributyl phosphate, phosphites, trimethyl phosphiteand tributyl phosphite, etc.

The polyester compositions of the present invention can be applied toeither single-layer or laminated films, but in view of film runningability and abrasion resistance, a laminated film containing at leastone layer made of the composition of the present invention ispreferable.

The laminated film in this specification refers to a film with at leasttwo layers in film thickness direction, and, therefore, includes a filmconsisting of three or more layers. Furthermore, it is preferable inview in view of film running ability that the outermost surface layer atleast on one side is made of the polyester composition of the presentinvention. A laminated film with layers made of the polyestercomposition of the present invention on both sides is especiallypreferable.

The laminated film can be composed variously. For example, a two-layerlaminated film can simply consist of a layer containing the crosslinkedpolymer particles of the present invention (layer X) and the other layer(layer Y), or the layer X may be coated on the surface with anotherlayer (e.g., good adhesive layer), or the layer Y may be coated on thesurface with another layer (e.g., good adhesive layer), or the surfaceof the layer Y may have a back coat layer. A three-layer laminated filmcan simply consist of layer X/layer Y/layer X, or the three-layerlaminated film can also be coated with another layer on the layer X ofone side, or coated with layers on the layers X of both sides (on bothsides of the laminated film). In this case, the thickness of a layer Xshould be preferably 0.01 to 3.0 μm, more preferably 0.05 to 2.0 μm,further more preferably 0.01 to 1.5 μm, and the thickness of the coatedlayer should be preferably 0.01 to 1.0 μm. Laminated films consisting offour or more layers simply have more layers Y (intermediate layers) inaddition to the above three-layer laminated film, and the positionalrelation between layers X and coated layers is the same as in thethree-layer laminated film. Furthermore, a laminated film usingdifferent layers on both outermost sides, for example, a three-layerlaminated film consisting of layer X/layer Y/layer Z can also be used.

In the laminated film as described above, the ratio of t/D, where t isthe thickness of the outermost layer (μm) and D is the average diameter(μm) of the crosslinked polymer particles of the present invention,should be preferably 0.1 to 10, more preferably 0.3 to 5, further morepreferably 0.5 to 3. Moreover, in the laminated film, it is preferablethat the number of protrusions on the surface of the outermost layer is3×10³ to 2×10⁵ mm², more preferably 5×10³ to 1.5×10⁵ /mm². Theprotrusions on the surface of the outermost layer refer to theprotrusions of 60 to 2000 nm in height. Furthermore, in the laminatedfilm, of the protrusions existing on the surface of the outermost layer,it is preferable that the number of protrusions of 0.7 to 2.6 μm indiameter is 100 to 10,000/mm², more preferably 300 to 9,000/mm², furthermore preferably 500 to 8,000/mm². The laminated film with t/D, thenumber of protrusions and the diameter of protrusions kept in the aboveranges is good in film slipperiness and abrasion resistance.

The method for producing such a laminated film is described belowconcretely. At first, the pellets of a polyester are mixed atpredetermined rates, and the mixtures are dried, supplied intoconventional melt lamination extruders, extruded as a sheet from a slitdie, and cooled and solidified on a casting roll, to prepare anon-stretched film. That is, two or more extruders and a two- ormore-layer manifold or feed block (e.g., feed block with a rectangularlaminating portion) are used for laminating, and a two- or more-layersheet is extruded from a die and cooled on a casting roll, to form anon-stretched film. In this case, installing a static mixer and a gearpump in the polymer passage or keeping the melting temperature ofextruder for extruding the polymer of the outermost layer at 5° to 10°C. lower than that for the base layer are effective to improve theuniformness of the film thickness.

Then, the non-stretched film is biaxially stretched, to be biaxiallyoriented. For stretching, either sequential biaxially stretching processor simultaneous biaxially stretching process can be used. However,sequential biaxially stretching process for at first stretching inlongitudinal direction and subsequently stretching in transversedirection with the stretching in longitudinal direction effected in 3 ormore stages with the total longitudinal stretching ratio kept at 3.5 to6.5 times is especially preferable. The longitudinal stretchingtemperature depends on the polyester used and cannot be specifiedgenerally, but it is usually effective to set the temperature at thefirst stage at 50° to 130° C., and those of the second and later stagesat higher than the temperature for the first stage. The longitudinalstretching speed should be preferably 5,000 to 50,000%/min. Thetransverse stretching is generally effected by using a stenter. Theproper stretching ratio is 3.0 to 5.0 times. The proper transversestretching speed is 1,000 to 20,000%/min., and the proper transversestretching temperature is 80° to 160° C. Subsequently, the stretchedfilm is heat-treated. The heat treatment temperature in this case shouldbe preferably 170° to 220° C., more preferably 180° to 200° C., and theheat treatment time should be preferably 0.2 to 20 seconds.

The surface roughness of the film should be preferably 40 or less, morepreferably 30 or less, further more preferably 20 or less in surfaceroughness parameter, Rt/Ra, which is the ratio of the maximum height,Rt, to the center line average height, Ra, in view of good abrasionresistance.

Furthermore, with regard to the distribution of surface protrusionheights in the film of the present invention, uniform protrusion heightsand good abrasion resistance can be achieved preferably if the relativestandard deviation of protrusion heights is 1.0 or less, where aprotrusion height is defined as the height of a 20 nm or higherprotrusion.

EXAMPLES

The present invention is described below in more detail in reference toexamples. Methods for measuring the respective physical values and themethods for evaluating the respective effects were as follows:

A. Particle Properties

(1) Particle Diameter

The particles in a polymer of film were photographed using an electronmicroscope at a magnification of about 20,000 to 50,000 times (30 photosof 8 cm×10 cm in size), and the equivalent sphere diameters of thecrosslinked polymer particles were measured. Then, weight averagediameter Dw, number average diameter Dn and Dw/Dn were calculated. Theequivalent sphere diameter refers to the diameter of a sphere with thesame volume as that of a particle.

(2) Thermal Decomposition Temperature of Particles

The curve of loss in weight of thermobalance was measured by TAS-100produced by Rigaku Denki in nitrogen gas atmosphere at a heating rate of20° C./min., and the 10% weight loss temperature was identified as thethermal decomposition temperature.

(3) Porosity

The pore volume of a particle was measured by a mercury porosimeter, andthe porosity was obtained from the following formula in reference to thepore volume and the specific gravity of the particle.

    Porosity(%)=Pore volume/{(1/Specific gravity)+Pore volume}×100

B. Polymer Property

(1) Intrinsic Viscosity

Measured with o-chlorophenol as the solvent at 25° C.

C. Film Properties

(1) Surface Roughness Parameters Ra and Rt

A high precision thin film level difference measuring apparatus, ET-10produced by Kosaka Kenkyuji was used for measurement. Ra is the centerline average roughness and Rt is the maximum height which expresses thedistance between the highest crest and the lowest trough in theroughness curve. The measurement was effected under the followingconditions, and the average value of 20 times of measurement wasadopted.

    ______________________________________                                        Probe tip radius:     0.5    μm                                            Probe load:           5      mg                                               Measured length:      1      mm                                               Cut off value:        0.08   mm                                               ______________________________________                                    

The respective parameters are defined in detail, for example, in JiroNara, "Methods for Measuring and Evaluating Surface Roughnesses (inJapanese)" (Sogo Gijutsu Center, 1983).

(2) Laminated Layer Thickness, t

When the particles contained most in a film were the crosslinked polymerparticles, the depth profile of the particle densities was measured byXPS (X-ray photoelectron spectrum), IR (infrared spectroscopic analysis)or confocal microscope, etc. with etching from the surface. In thesurface layer in a film with a laminated layer on one side, the particledensity is low because of the interface called the surface, and theparticle density becomes higher according to the increase in distancefrom the surface.

In a film with a laminated layer on one side of the present invention,the particle density once becomes maximum at depth [I] and begins todecrease again. Based on the particle density curve, the depth [II](II>1) at which the particle density is 1/2 of the maximum value isdefined as the laminated layer thickness, t. For other laminated films,similar analysis was made starting from the portion where the particledensity began to appear. When inorganic particles, etc. were contained,the density of the element concerned with the particles with the highestdensity among the particles of the film was measured using a secondaryion mass spectrum (SIMS) instrument, and ratio of the density to thedensity of the carbon element in the polyester (M⁺ /C⁺) was identifiedas the particle density. Analysis was effected in the depth (thickness)direction from the surface of the layer X of polyester, and as doneabove, the laminated layer thickness, t can be obtained. Furthermore, itcan also be obtained by observing the cross section of a film or using alevel difference measuring apparatus.

(3) Running Ability

A slit film with a width of 1/2 inch was run using a tape runningtester, Model TBT-300 (produced by K. K. Yokohama System Kankyujo) at20° C. and 60% RH, and the initial friction coefficient μk was obtainedfrom the following formula. The guide diameter was 6 mm, and the guidematerial was SUS 27 (surface roughness 0.2S). The winding angle was 180°and the running speed was 3.3 cm/sec.

    μk=0.733×log (T.sub.1 /T.sub.2)

    T.sub.1 : Outgoing-side tension

    T.sub.2 : Incoming-side tension

If the above μk is 0.35 or less, the film is good in slipperiness. If μkis larger than 0.35, slipperiness is very poor during film production oras a film product.

(4) Number, Heights and Diameters of Protrusions on the Surface of aFilm

A two-detector type scanning electron microscope (ESM-3200 produced byElionics Corporation) and a cross section measuring apparatus (PMS-1produced by Elionics Corporation) were used to measure the heights ofprotrusions by scanning with the height of the flat face on the surfaceof a film as 0, and the measured values were applied to an imageprocessor (IBAS-2000 produced by Karlzuis Corporation), forreconstructing a film surface protrusion image on the image processor.On the surface protrusion image, the protrusion portions were processedinto binary numbers for obtaining the areas of the individualprotrusions. From the areas, equivalent circle diameters were obtainedto be adopted as protrusion diameters, and the number of protrusions of0.7 to 2.6 μm in diameter was counted. Furthermore, the highest value ofthe binary numbers obtained from each protrusion portion was identifiedas the height of the protrusion. The measurement was effected 500 timesat different places, and protrusions of 10 nm or more in height wereidentified as protrusions. Of the measured protrusions, the averagevalue of their heights was identified as the average height. Themagnification of the scanning electron microscope was selected in arange from 1,000 to 8,000 times, to measure the number of protrusionsexceeding 60 nm, and the magnification of the scanning electronmicroscope was selected in a range from 10,000 to 50,00 times, to countthe number of protrusions. As the case may be, the height informationobtained by using a high precision light interference typethree-dimensional surface analyzer (TOPO-3D produced by WYKOCorporation, with an objective lens of 40 to 200 magnifications using ahigh resolution camera is effective) can be adopted instead of thevalues of said SEM.

(5) Abrasion Resistance (High Speed Running)

A tape roll of a slit film of 1/2 inch was rubbed against a guide rollmade of stainless steel SUS-304 at a winding angle of 60° at a speed of250 m/min. at a tension of 95 g for 500 m, to judge the abrasionresistance in reference to the white powder generated on the surface ofthe guide roll according to the following criterion. Grades A and B areacceptable.

Grade A . . . No white powder was generated at all.

Grade B . . . Some white powder was generated.

Grade C . . . Rather much white powder was generated.

Grade D . . . Much white powder was generated.

(6) Magnetic Face Flaw Preventability

A marketed video tape was longitudinally wound around a pin of 7 mm indiameter at a tension of 100 g with the magnetic face as the surface.Furthermore, a slit sample film of 1/2 in width was wound longitudinallyto overlap the video tape at a winding angle of 120° at a tension of 50g, and the sample film was reciprocated for a distance of 5 cm ten timesat a running speed of 200 cm/min. The flaws caused on the magnetic facein this case were observed by a differential interference microscope ata magnification of 50 times. When few flaws were caused, the film wasjudged to be good in magnetic face flawing preventability, and when 20or more flaws were caused, the film was judged to be poor in magneticface flaw preventability.

(7) Electromagnetic Conversion Property

A film was coated with a magnetic coating solution composed as followsby a gravure roll, magnetically oriented and dried. Furthermore, it wascalendered by a small test calender (steel roll/nylon roll, 5 steps) at70° C. at a linear pressure of 200 kg/cm, and cured at 70° C. for 48hours. The raw tape was slit at a width of 1/2 inch, and a pancake wasprepared. The pancake was incorporated into a 250 m long VTR cassette,for use as a VRT cassette tape.

    ______________________________________                                        (Composition of magnetic coating solution)                                    ______________________________________                                        Cobalt-containing iron oxide:                                                                        100 parts by weight                                    Vinyl chloride/vinyl acetate copolymer:                                                               10 parts by weight                                    Polyurethane elastomer:                                                                               10 parts by weight                                    Polyisocyanate:         5 parts by weight                                     Lecithin:               1 part by weight                                      Methyl ethyl ketone:    75 parts by weight                                    Methyl isobutyl ketone:                                                                               75 parts by weight                                    Toluene:                75 parts by weight                                    Carbon black:           2 parts by weight                                     Lauric acid:            1.5 parts by weight                                   ______________________________________                                    

The tape was used in a household VTR to record 100% chromatic signalsusing a television testing wave generator, and from the reproducedsignals, chromatic S/N was measured using a color video noise measuringinstrument.

EXAMPLE 1

One hundred parts by weight of dimethyl terephthalate, 70 parts byweight of ethylene glycol, 0.06 part by weight of magnesium acetate asan ester interchange catalyst, 0.03 part by weight of antimony trioxideas a polymerization catalyst and 0.03 part by weight of trimethylphosphate as a thermal stabilizer were used to obtain a polyethyleneterephthalate (I) of 0.65 dl/g in intrinsic viscosity not containingparticles according to an ordinary method. The polyethyleneterephthalate (I) was molten using a vent type twin-screw extruder, anda water slurry containing 20 wt % of crosslinked polymer particlescomposed of maleic acid/bisphenol A/styrene (1:1:1 as molar ratio) of0.3 μm in number average diameter D, 1.3 in Dw/Dn, 70% in porosity and400° C. in thermal decomposition temperature obtained by suspensionpolymerization was added to have 0.35 wt % of the crosslinked polymerparticles contained in the polyester composition. With the vent holekept at a vacuum degree of 10 Torrs, the mixture was melt-extruded at aresin temperature of 280° C., to obtain a polyethylene terephthalatecomposition containing the crosslinked polymer particles. The intrinsicviscosity of the polymer obtained was 0.62 dl/g.

Then, the polyethylene terephthalate composition was dried under reducedpressure at 180° C. for 3 hours, and melt-extruded at 290° C. and formedinto a non-stretched film using the electrostatic casting method.Subsequently it was stretched to 4 times in longitudinal direction and3.6 times in transverse direction, and heat-treated at 200° C. for 5seconds with the size kept constant, to obtain a 13 μm thick film. Thefilm was 0.013 in Ra, 0.25 in Rt, 0.22 in running ability μk, Grade A inabrasion resistance and good in magnetic face flaw preventability asshown in Table 1.

EXAMPLE 2

A film was obtained as done in Example 1, except that the crosslinkedpolymer particles used were made of an unsaturated polyester resincomposed of maleic acid/ethylene glycol/styrene (1:1:1 as molar ratio)of 0.3 μm in number average diameter D, 1.3 in Dw/Dn, 65% in porosityand 390° C. in thermal decomposition temperature obtained by suspensionpolymerization. The film was good in running ability, abrasionresistance and magnetic face flaw preventability as shown in Table 1.

EXAMPLE 3

A polyethylene terephthalate composition was obtained as done in Example1, except that the crosslinked polymer particles used were made of anunsaturated polyester resin composed of maleic acid/ethyleneglycol/glycidyl methacrylate/styrene (2:2:1:1 as molar ratio) of 0.8 μmin number average diameter D, 1.4 in Dw/Dn, 70% in porosity and 390° C.in thermal decomposition temperature obtained by emulsionpolymerization. The film was good in properties as shown in Table 1.Since the particles were obtained by emulsion polymerization, runningability and abrasion resistance were somewhat lower.

EXAMPLE 4

One hundred parts by weight of dimethyl terephthalate, 70 parts byweight of ethylene glycol, 0.1 part by weight of calcium acetate and 0.2part by weight of lithium acetate as an ester interchange catalyst, 0.03part by weight of antimony trioxide as a polymerization catalyst, 0.15part by weight of trimethyl phosphate and 0.02 part by weight ofphosphorous acid as a thermal stabilizer were used to obtain apolyethylene terephthalate composition (II) of 0.65 dl/g in intrinsicviscosity containing non-incorporated particles according to an ordinarymethod. Then, crosslinked polymer particles composed of maleicacid/fumaric acid/ethylene glycol/styrene (1:1:2:2 as molar ratio) of0.2 μm in number average diameter D, 1.2 in Dw/Dn, 60% in porosity and395° C. in thermal decomposition temperature obtained by suspensionpolymerization were added to the polyethylene terephthalate composition(II), to obtain a film as done in Example 1. The film was good inrunning ability, abrasion resistance and magnetic face flawpreventability as shown in Table 1.

EXAMPLE 5

Zirconium oxide of 0.03 μm in number average diameter was used asinorganic particles, and an ethylene glycol slurry of it was added aftercompletion of ester interchange reaction, to obtain a polyethyleneterephthalate composition (III) according to an ordinary method. Then,crosslinked polymer particles composed of terephthalicacid/propenediol/divinylbenzene of 0.5 μm in number average diameter D,1.5 in Dw/Dn, 65% in porosity and 395° C. in thermal decompositiontemperature were added to the polyethylene terephthalate composition(III) using a vent type twin-screw extruder, to obtain a film as done inExample 1. The film was good in abrasion resistance and magnetic faceflaw preventability as shown in Table 1.

COMPARATIVE EXAMPLE 1

A film was prepared as done in Example 1, except that crosslinkedpolymer particles composed of divinylbenzene/ethylvinylbenzene (1:1 asmolar ratio) of 0.3 μm in number average diameter D, 2.0 in Dw/Dn, 35%in porosity and 390° C. in thermal decomposition temperature produced byemulsion polymerization were used. Since the crosslinked polymerparticles did not have ester bonds, the film was poor in running abilityand abrasion resistance as shown in Table 2.

COMPARATIVE EXAMPLE 2

A film was obtained as done in Example 1, except that silicon dioxideparticles of 0.5 μm in number average diameter D, 1.0 in Dw/Dn and 10%in porosity were used. Since inorganic particles were used, they werelow in affinity, and the film was poor in running ability, abrasionresistance and magnetic face flaw preventability as shown in Table 2.

EXAMPLE 6

The crosslinked polymer particles shown in Table 3 were used to obtain apolyethylene terephthalate composition as down in Example 1. Thepolyethylene terephthalate composition and the polyethyleneterephthalate (I) were dried under reduced pressure at 180° C. for 3hours. Then the two polymers were supplied into respectively differentextruders, molten at 290° C., highly accurately filtered while beinglaminated using a three-layer feed block with a rectangular laminatingportion into a three-layer structure consisting of the polyethyleneterephthalate (I) as the base layer and the polyethylene terephthalatecomposition as the surface layers on both sides, further extruded into asheet from a fish tail type die, and wound around a casting drum of 30°C. in surface temperature, to be cooled and solidified using theelectrostatic casting method, for producing an about 160 μm thicknon-stretched film. The draft ratio was 6.5.

The non-stretched film was stretched in 3 stages in longitudinaldirection to 1.2 times at 123° C. 1.45 times at 126° C. and 2.3 times at114° C. respectively. The monoaxially stretched film was stretched intransverse direction using a stenter to 3.5 times at 111° C., andheat-treated at 200° C. for 5 seconds with the size kept constant, toobtain a 13 μm thick film (laminated layer thickness t=1.0 μm, t/D=2.5).As shown in Table 3, the content of the crosslinked polymer particles inthe outermost surfaces of the obtained film was 0.36 wt %, and the filmwas good in running ability, abrasion resistance and magnetic faceflawing preventability. The electromagnetic conversion property wasmeasured and the chromatic S/N ratio was found to be +2.0 dB inreference to Example 5.

As described above, a film with a polyester composition containing thecrosslinked polymer particles of the present invention laminated as theoutermost surface layers can be good also in electromagnetic conversionproperty.

EXAMPLE 7

The crosslinked polymer particles shown in Table 3 were used to obtain alaminated film as done in Example 6. The film was good in runningability, abrasion resistance, magnetic face flawing preventability andelectromagnetic conversion property as shown in Table 3.

COMPARATIVE EXAMPLES 3 AND 4

The crosslinked polymer particles or inorganic particles shown in Table3 were used to obtain laminated films as done in Example 6. ComparativeExample 3 used particles without ester bonds at the main chain andComparative Example 4 used inorganic particles low in affinity. So, asshown in Table 3, the films were poor in running ability, abrasionresistance, magnetic face flaw preventability and electromagneticconversion property.

EXAMPLE 8

A film was obtained as done in Example 1, except that crosslinkedpolymer particles of 0.3 μm in number average diameter D, 1.5 in Dw/Dn,65% in porosity and 385° C. in thermal decomposition temperatureobtained from terephthalic acid and pentaerythritol by condensationpolymerization were used. The film was good in running property,abrasion resistance and magnetic face flaw preventability as shown inTable 4.

EXAMPLES 9 AND 10

Films were obtained as done in Example 1, except that particlesdifferent in composition, number average diameter, Dw/Dn, porosity,thermal decomposition temperature and content were used. These filmswere good in abrasion resistance and magnetic face flaw preventabilityas shown in Table 4. However, since particles rather low in thermaldecomposition temperature were used in Example 10, the film was somewhatlower in abrasion resistance.

EXAMPLE 11

A film was obtained as done in Example 4 by letting the polyethyleneterephthalate (II) containing non-incorporated particles contain thecrosslinked polymer particles shown in Table 4. The film was good inrunning ability, abrasion resistance and magnetic face flawpreventability as shown in Table 4.

EXAMPLE 12

A film was obtained as done in Example 5 by letting the polyethyleneterephthalate (III) containing zirconium oxide contain the crosslinkedpolymer particles shown in Table 4. The film was food in runningability, abrasion resistance and magnetic face flaw preventability asshown in Table 4.

COMPARATIVE EXAMPLES 5 AND 6

The particles shown in Table 5 were used to obtain films as done inExample 1. Since the particles were made of a non-crosslinked linearpolyester, the films were poor in running ability, abrasion resistanceand magnetic face flaw preventability as shown in Table 5.

EXAMPLES 13 and 14

The crosslinked polymer particles shown in Table 6 were used to obtainlaminated films as done in Example 6. The films were good in runningability, abrasion resistance, magnetic face flawing preventability andelectromagnetic conversion property as shown in Table 6.

COMPARATIVE EXAMPLE 7

The particles shown in Table 6 were used to obtain a laminated film asdone in Example 6. Since the particles were made of a non-crosslinkedlinear polyester, the film was poor in running ability, abrasionresistance, magnetic face flaw preventability and electromagneticconversion property as shown in Table 6.

                                      TABLE 1                                     __________________________________________________________________________           Properties                                                                             Example 1                                                                             Example 2                                                                             Example 3                                                                             Example 4                                                                              Example                      __________________________________________________________________________                                                     5                            Particles                                                                            Composition                                                                            Maleic acid/                                                                          Maleic acid/                                                                          Maleic acid/                                                                          Maleic acid/                                                                           Terephthalic                                 bisphenol A/                                                                          ethylene                                                                              ethylene                                                                              fumaric acid/                                                                          acid/                                        styrene glycol/styrene                                                                        glycol/ ethylene propenediol/                                                 glycidyl                                                                              glycol/styrene +                                                                       divinylbenzene +                                             methacrylate/                                                                         non-     zirconium                                                    styrene incorporated                                                                           oxide                                                                particles                                    Molar ratio of                                                                         1:1:1   1:1:1   2:2:1:1 1:1:2:2  1:1:1                               components                                                                    Production                                                                             Suspension                                                                            Suspension                                                                            Emulsion                                                                              Suspension                                                                             Suspension                          method   polymerization                                                                        polymerization                                                                        polymerization                                                                        polymerization                                                                         polymerization                      Average  0.3     0.3     0.8     0.2      0.5/0.03                            diameter (μm)                                                              Dw/Dn    1.3     1.3     1.4     1.2      1.5                                 Porosity (%)                                                                           70      65      70      60       65                                  Heat     400     390     390     395      395                                 decomposition                                                                 temperature (°C.)                                                      Content (wt %)                                                                         0.35    0.35    0.32    0.38     0.30/0.03                    Composition                                                                          Intrinsic                                                                              0.62    0.62    0.62    0.61     0.62                         material                                                                             viscosity (dl/g)                                                       Film   Ra (μm)                                                                             0.013   0.015   0.017   0.012    0.014                        properties                                                                           Rt (μm)                                                                             0.25    0.27    0.29    0.21     0.26                                Running ability                                                                        0.22    0.24    0.30    0.25     0.24                                (μk)                                                                       Abrasion Grade A Grade A Grade B Grade A  Grade A                             resistance                                                                    Magnetic face                                                                          Good    Good    Good    Good     Good                                flaw                                                                          preventability                                                         __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________            Properties   Comparative example 1                                                                     Comparative example 2                        __________________________________________________________________________    Particles                                                                             Composition  Divinylbenzene/ethyl                                                                      silicon dioxide                                                   vinylbenzene                                                     Molar ratio of components                                                                  1:1         --                                                   Production method                                                                          Emulsion polymerization                                                                   --                                                   Average diameter (μm)                                                                   0.3         0.5                                                  Dw/Dn        2.0         1.0                                                  Porosity (%) 35          10                                                   Heat decomposition                                                                         390         --                                                   temperature (°C.)                                                      Content (wt %)                                                                             0.35        0.30                                         Composition                                                                           Intrinsic viscosity (dl/g)                                                                 0.62        0.62                                         material                                                                      Film properties                                                                       Ra (μm)   0.015       0.020                                                Rt (μm)   0.30        0.27                                                 Running ability (μk)                                                                    0.29        0.30                                                 Abrasion resistance                                                                        Grade C     Grade D                                              Magnetic face flaw                                                                         Good        Poor                                                 preventability                                                        __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________                                         Comparative                                                                            Comparative                            Properties  Example 6                                                                              Example 7                                                                              example 3                                                                              example 4                       __________________________________________________________________________    Particles                                                                            Composition Fumaric acid/                                                                          Maleic acid/                                                                           methyl   calcium carbonate                                  ethylene glycol/                                                                       ethylene glycol/                                                                       methacrylate/                                               divinylbenzene                                                                         ethylene glycol                                                                        butyl acrylate/                                                      dimethacrylate                                                                         divinylbenzene                                  Molar ratio of                                                                            1:1:1    1:1:1    1:1:2    --                                     components                                                                    Production method                                                                         Suspension                                                                             Suspension                                                                             Emulsion --                                                 polymerization                                                                         polymerization                                                                         polymerization                                  Average diameter (μm)                                                                  0.4      0.5      0.4      0.5                                    Dw/Dn       1.4      1.2      1.5      5.5                                    Porosity (%)                                                                              70       65       40       15                                     Heat decomposition                                                                        395      390      390      --                                     temperature (°C.)                                                      Content (wt %)                                                                            0.36     0.33     0.35     0.30                            Composition                                                                          Intrinsic viscosity                                                                       0.62     0.62     0.61     0.62                            matenal                                                                              (dl/g)                                                                 Film   Laminated layer                                                                           1.0      1.2      1.0      1.2                             properties                                                                           thickness t (μm)                                                           Ra (μm)  0.024    0.023    0.029    0.030                                  Rt (μm)  0.24     0.23     0.31     0.30                                   Protrusions 2.0 × 10.sup.4                                                                   1.8 × 10.sup.4                                                                   1.0 × 10.sup.4                                                                   0.8 × 10.sup.4                   (number/mm.sup.2)                                                             Protrusions with 0.7-                                                                      3,000   3,200    2,500    12,000                                 2.6 μm diameter                                                            (number/mm.sup.2)                                                             Running ability (μk)                                                                   0.21     0.20     0.31     0.34                                   Abrasion resistance                                                                       Grade A  Grade A  Grade D  Grade D                                Magnetic face flaw                                                                        Good     Good     Poor     Poor                                   preventability                                                                Electromagnetic                                                                           +2.0     +1.8     -0.3     -0.5                                   conversion property                                                           (dB)                                                                   __________________________________________________________________________     Electromagnetic conversion property is calculated in reference to Example     5.                                                                       

                                      TABLE 4                                     __________________________________________________________________________           Properties                                                                             Example 8                                                                             Example 9                                                                            Example 10                                                                            Example 11                                                                            Example 12                     __________________________________________________________________________    Particles                                                                            Composition                                                                            Terephthalic                                                                          Terephthalic                                                                         Isophthalic                                                                           pyromellit                                                                            2,6-naphthale-                                 acid/   acid/  acid/trimellitic                                                                      acid/ethylene                                                                         nedicarboxylic                                 pentaerythritol                                                                       trimethylol-                                                                         acid/ethylene                                                                         glycol + non-                                                                         acid/glycerin +                                        propane                                                                              glycol  incorporated                                                                          zirconium                                                             particles                                                                             oxide                                 Molar ratio of                                                                         1:1     1:1    1:2:3   1:1     1:1                                   components                                                                    Average  0.3     0.3    1.0     0.2     0.5/0.03                              diameter (μm)                                                              Dw/Dn    1.5     1.4    1.4     1.3     1.7                                   Porosity (%)                                                                           65      60     50      40      55                                    Heat     385     380    370     385     385                                   decomposition                                                                 temperature (°C.)                                                      Content (wt %)                                                                         0.30    0.3    0.25    0.35    0.30/0.03                      Composition                                                                          Intrinsic                                                                              0.62    0.61   0.62    0.62    0.62                           material                                                                             viscosity (dl/g)                                                       Film   Ra (μm)                                                                             0.016   0.015  0.021   0.013   0.017                          properties                                                                           Rt (μm)                                                                             0.25    0.24   0.40    0.23    0.26                                  Running ability                                                                        0.23    0.26   0.28    0.27    0.25                                  (μk)                                                                       Abrasion Grade A Grade A                                                                              Grade B Grade A Grade A                               resistance                                                                    Magnetic face                                                                          Good    Good   Good    Good    Good                                  flawing                                                                       preventability                                                         __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________            Properties   Comparative example 6                                                                     Comparative example 7                        __________________________________________________________________________    Particles                                                                             Composition  Terephthalic acid/                                                                        2,6-naphthalenedicarboxylic                                       1,4-cyclohexadimethanol                                                                   acid/ethylene glycol                                 Molar ratio of components                                                                  1:1         1.1                                                  Average diamter (μm)                                                                    0.3         0.4                                                  Dw/Dn        1.3         6.0                                                  Porosity (%) 15          30                                                   Heat decomposition                                                                         355         360                                                  temperature (°C.)                                                      Content (wt %)                                                                             0.35        0.30                                         Composition                                                                           Intrinsic viscosity (dl/g)                                                                 0.62        0.62                                         material                                                                      Film properties                                                                       Ra (μm)   0.023       0.025                                                Rt (μm)   0.31        0.35                                                 Running ability (μk)                                                                    0.32        0.33                                                 Abrasion resistance                                                                        Grade D     Grade D                                              Magnetic face flaw                                                                         Poor        Poor                                                 preventability                                                        __________________________________________________________________________

                                      TABLE 6                                     __________________________________________________________________________                                            Comparative                                   Properties  Example 13 Example 14                                                                             example 7                             __________________________________________________________________________    Particles                                                                             Composition Trimellitic acid/1,4-                                                                    Trimellitic                                                                            Terephthalic                                              cyclohexadimethanol                                                                      acid/bisphenol A                                                                       acid/isophthalic                                                              acid/bisphenol A                              Molar ratio of                                                                            1:1        1:1      4:1:5                                         components                                                                    Average diameter (μm)                                                                  0.4        0.5      0.4                                           Dw/Dn       1.2        1.4      5.5                                           Porosity (%)                                                                              65         70       25                                            Heat decomposition                                                                        390        395      345                                           temperature (°C.)                                                      Content (wt %)                                                                            0.35       0.32     0.33                                  Composition                                                                           Intrinsic viscosity                                                                       0.62       0.61     0.62                                  material                                                                              (dl/g)                                                                Film properties                                                                       Laminated layer                                                                           1.0        1.2      1.0                                           thickness t (μm)                                                           Ra (μm)  0.021      0.023    0.030                                         Rt (μm)  0.24       0.22     0.29                                          Protrusions 2.1 × 10.sup.4                                                                     2.0 × 10.sup.4                                                                   0.9 × 10.sup.4                          (number/mm.sup.2)                                                             Protrusions with 0.7-                                                                     2,800      2,900    1,200                                         2.6 μm diameter                                                            (number/mm.sup.2)                                                             Running ability (μk)                                                                   0.23       0.24     0.33                                          Abrasion resistance                                                                       Grade A    Grade A  Grade D                                       Magnetic face flawing                                                                     Good       Good     Poor                                          preventability                                                                Electromagnetic                                                                            +1.8      +2.0     -0.6                                          conversion property                                                           (dB)                                                                  __________________________________________________________________________     Electromagnetic conversion property is calculated in reference to Example     5.                                                                       

INDUSTRIAL APPLICATIONS OF THE INVENTION

The thermoplastic polyester compositions of the present inventioncontain crosslinked polymer particles excellent in affinity topolyesters. So, the films formed from the polyester compositions arehard to cause the particles to fall off during high speed running andhard to cause the particles to flaw magnetic faces. Therefore, thepresent invention can prevent the generation of white powder and theflawing of magnetic faces caused by falling-off particles, so as toavoid contamination caused during film production, and is especiallysuitable for use as products such as magnetic tapes.

We claim:
 1. A polyester composition comprising crosslinked polymerparticles with an ester bond at the main chain, said particles includingat least a polyester formed from a polybasic acid or any of its esterformable derivatives and a polyhydric alcohol.
 2. A polyestercomposition, according to claim 1 wherein the main chain of thecrosslinked polymer particles is an unsaturated polyester resin with adicarboxylic acid and a glycol as main components, at least either ofthe components having at least one aliphatic unsaturated bond, andcrosslinked by a compound with at least one aliphatic unsaturated bond.3. A polyester composition according to claim 1 wherein at least eitherof the polybasic acid or polyhydric alcohol comprise tri-orhigher-valent.
 4. A polyester composition, according to claim 1 whereinthe crosslinked polymer particles are produced by suspensionpolymerization.
 5. A polyester composition, according to claim 2,wherein the main chain of the crosslinked polymer particles is mainlycomposed of a dicarboxylic acid and a glycol, at least either of thecomponents having one vinyl group, and crosslinked by a compound withone or two vinyl groups.
 6. A polyester composition, according to claim5, wherein the said crosslinked polymer particles are composed of maleicacid and/or fumaric acid as a main carboxylic acid component, and acompound selected from a group consisting of propenediol, butenediol,pentyl glycol, neopentyl glycol and bisphenol A as a main glycolcomponent, with a compound selected from a group consisting of styrene,acrylic acid, diacrylic acid, methacrylic acid and dimethacrylic acid asa main crosslinking component.
 7. A polyester composition, according toclaim 5, wherein the said crosslinked polymer particles are composed ofmaleic acid and/or fumaric acid, and isophthalic acid and/orterephthalic acid as a main dicarboxylic acid components, and bisphenolA as a main glycol component, with styrene as a main crosslinkingcomponent.
 8. A polyester composition, according to claim 3, wherein thepolybasic acid and the polyhydric alcohol comprise at least eithertrivalent to tetravalent.
 9. A polyester composition, according to claim8, wherein the said crosslinked polymer particles are made of apolyester resin composed of a compound selected from a group consistingof terephthalic acid, isophthalic acid, maleic acid, trimesic acidtrimellitic acid and pyromellitic acid as a main polybasic acidcomponent, and a compound selected from a group consisting of ethyleneglycol, cyclohexanedimethanol, bisphenol A, glycerol, trimethylolpropaneand pentaerythritol as a main polyhydric alcohol component.
 10. Apolyester composition, according to claim 9, wherein the saidcrosslinked polymer particles are made of a polyester resin composed oftrimetallitic acid and/or pyromellitic acid as a main polybasic acidcomponent, and glycerol and/or pentaerythritol as a main polyhydricalcohol component.
 11. A polyester composition, according to claim 1wherein the crosslinked polymer particles are 0.01 to 5 μm in averagediameter and 0.005 to 10 wt % in content.
 12. A polyester composition,according to claim 1 wherein the crosslinked polymer particles are morethan 1.1 to less than 5.0 in ratio Dw/Dn, wherein Dw is the weightaverage diameter and Dn is the number average diameter.
 13. A polyestercomposition, according to claim 1 wherein the crosslinked polymerparticles are 350° C. or higher in thermal decomposition temperature.14. A polyester composition, according to claim 1 wherein thecrosslinked polymer particles are 20 to 95% in porosity.
 15. A polyestercomposition, according to claim 1 wherein a slurry of the crosslinkedpolymer particles in water and/or an organic compound of 200° C. orlower in boiling point is added to a polyester by using a vent typemolding machine.
 16. A polyester composition, according to claim 1,wherein inactive inorganic particles and/or organic particles of 0.001to 3 μm in average diameter are contained by 0.01 to 10 wt %.
 17. Afilm, comprising the polyester composition state in claim
 1. 18. Alaminated film, comprising at least one layer made of the polyestercomposition stated in claim
 1. 19. A laminated film, according to claim18, wherein the layer made of the said polyester composition is arrangedat lest as the outermost layer on one side of the said laminated film.20. A laminated film, according to claim 19, wherein the ratio t/D,where t represents the thickness of the outermost layer, and Drepresents the average diameter of the crosslinked polymer particles, is0.1 to
 10. 21. A laminated film, according to claim 19 or 20, whereinthe number of the protrusions on the surface of the outermost layer is3×10³ to 2×10⁵ /mm².
 22. A laminated film, according to claim 19 whereinthe number of protrusions of 0.7 to 2.6 μm in diameter among protrusionsexisting on the outermost layer is 100 to 10,000/mm².
 23. A film,according to claim 17 used as a base film for magnetic recording medium.